The need for and use of prosthetic hands has been around for centuries. Even today with advancing technologies, the use of the inefficient prosthetic devices is critical as several thousands of people in the United States alone have entire arm amputations and partial/complete hand amputations. After the loss of a limb, a significant part of a patient's recovery and resumption of daily activities is dependent upon the use of a prosthetic device. This recovery becomes more complex when the loss is of an entire hand. In the last twenty years, the prosthetics design and technology has seen major improvements, allowing for more functionality and increased dexterity for upper limp amputees. However, still, there are major needs that can be addressed to further the advancement of prosthetic hand designs to allow prosthetic hand users to have capabilities similar to those of an innate human hand.
Despite attempts to mimic the natural mechanisms of the hand, existing hand models lack dexterity and functionality and are underactuated, bulky, and expensive. The current art does not focus on these shortcomings of the prosthetic itself, but rather on improving the technology used to control prosthetic hand devices. This involves applications that are centered on Brain Computer Interfaces (BCI), signal processing, and feedback control mechanisms. These applications create an interface between the amputee and the prosthetic device and allow users to apply various forces and different grasps that are needed in everyday activities via electromyography technology. These “myoelectric” prosthetic hands use sensors strategically placed on the residual limb to detect muscle contractions that translate into finger movements of the hand. Myoelectric designs that are currently on the market and are reflective of the current state of the art include the Vincent Hand by Vincent Systems, i-Limb Hand by Touch Bionics, i-Limb Pulse by Touch Bionics, BeBionic Hand by RSL Steeper, BeBionic Hand v2 by RSL Steeper, and the Michelangelo Hand by Otto Bock. However, more traditional body powered devices are more accepted than the newer myoelectric designs due to major technology gaps that exist to make these “myoelectric” hands more efficient and feasible for amputees to use.
Problems in the current art with current models include: (1) the weight of the prosthetic device; (2) the cosmetic appearance of the prosthetic; (3) the grasping forces and speeds presently in the art; (4) needed noise reduction; and (5) increased functionality. These “technology gaps” exist due to the difficulty of creating an artificial hand that closely mimics the innate abilities of the natural human hand while keeping the design parameters within reasonable confines of the hand's relative anatomical features (e.g., weight, size, and cosmetic appearance). Addressing all of the needs is challenging and can be generalized by improving the overall driving mechanism of the prosthetic device since the driving mechanism does encompass issues related to device weight, force, speed, noise, and overall functionality.
The driving mechanism of prosthetic hands manipulates the digits of the hand, individually or together, to allow the user to undertake various activities. Several deficiencies of currently available artificial hands relate to the driving mechanisms of these devices, so improving on the design of the mechanism can address these needs and can allow for greater manipulation and dexterity of the prosthetic device by the end user. Several driving mechanisms are currently used to operate prosthetic designs, and each uses a different technique to provide motion to the digits of the prosthetic device. These mechanisms can be classified into one of six categories: (1) body-driven; (2) pneumatic; (3) hydraulic; (4) cable transmission; (5) multiple transmissions; and (6) hybrid combinations.
Body-driven prosthetic devices for upper limb amputees consists of a body harness connected to a cable that leads to the end of the device where the cable is than usually connected to a 2 digit pinching mechanism. The apparatus can be opened or closed by moving the opposing shoulder unto which the harness is fastened. They are cheap, lightweight, durable, and easily assembled, but they have limited grasping capabilities, are awkward in appearance, and constrict the body when in use.
Pneumatic driving mechanisms use a fluid actuator element to provide motion to the digits of a prosthetic hand. These actuator elements contain several parts including a feed channel, fluid pump, and an air chamber that is connected to the movable joints of a prosthetic hand. When the elements are inflated with air, the volume of the elements expands and causes movement of the finger. Pneumatic designs are capable of being small and lightweight with comparable grasping forces to a human hand, but they require large amounts of power to operate and produce loud hissing sounds when in operation.
The hydraulic mechanism has the same advantages of the pneumatic mechanism with added qualities. The hydraulic mechanism uses fluid actuators, but it also contains a multi-valve micro pump with an attached fluid reservoir that allows fluid to be transferred to several elements to move several fingers at the same time. Movement is basically the same in both mechanisms with movement of device caused by the expansion of several actuator elements. The hydraulic mechanism has a lower energy consumption and greater grasping forces than the pneumatic design without the hissing sounds from the actuators. The mechanism has dual functions and can be operated with air or liquid, but weight issues and the potential of hydraulic fluids leaking from the elements causing detrimental damage to the electronic controls is too risky.
Cable transmission mechanisms consist of a combination of cables and pulleys located in the joints of the artificial fingers of the prosthetic hand. The pulleys are operated by servomotors that can turn the pulleys allowing movement of the fingers. These mechanisms are also considered to be lightweight and small with similar grasping forces compared to the hydraulic designs but have limited ability and maintenance issues due to the number of moving parts.
The multiple transmission mechanism is a hybrid mechanism that uses various approaches to provide motion to the fingers of the prosthetic device, and many driving mechanisms fall under this category. However, each mechanism contains but is not limited to a motor and actuator system that is linked to a gearbox which in turn rotates a driveshaft. They work in a manner similar to the cable transmission design but include a blocking system that locks pulleys in place to allow for a position to be held. This design allows for multiple pulleys to be operated by one motor, which can reduce the weight of the hand, but it also reduces the grasping force of the hand since each finger is coupled to the same motor.
The hybrid option is a mixture between the body-powered prosthesis and the externally powered driving mechanism. The most common combination is the use of a body-powered elbow with an electric hand or wrist or an electric elbow with a body-powered hand.
Each mechanism has its advantages and disadvantages depending on the individual user and the intended use of the device. Yet, major technology gaps exist that prevent a more efficient and complete mechanism to be implemented into a prosthetic hand to allow for individual manipulation of all 5 digits including automated thumb rotation. The new technology disclosed herein is an electromagnetic driving mechanism for a prosthetic hand device that fills the current technology gaps in the prosthetic hand industry.